THE ROLE OF THE LOW-TEMPERATURE BUFFER LAYER AND LAYER THICKNESS IN THE OPTIMIZATION OF OMVPE GROWTH OF GAN ON SAPPHIRE

In agreement with previous Work,(1,2) a thin, low temperature GaN buff er layer, that is used to initiate OMVPE growth of GaN growth on sapph ire, is shown to play a critical role in determining the surface morph ology of the main GaN epilayer. X-ray analysis shows that the mosaicit y of the main GaN epilayer continues to improve even after several mu m of epitaxy. This continuing improvement in crystal perfection correl ates with an improvement in Hall mobility for thicker samples. So far, we have obtained a maximum mobility of 600 cm(2)/V-s in a 6 mu m GaN epilayer. Atomic farce microscopy (AFM) analysis of the buffer layer a nd x-ray analysis of the main epilayer lead us to conclude that the bo th of these effects reflect the degree of coherence in the main GaN ep itaxial layer. These results are consistent with the growth model pres ented by Hiramatsu et al., however, our AFM data indicates that for Ga N buffer layers partial coherence can be achieved during the low tempe rature growth stage.